Campbell Scientific LI200X-L LI-COR Silicon Pyranometer - Manual (Page 16)

Appendix A. LI200S Pyranometer
A-2
A.3 Input Range
The following is an example of how to determine the optimum input range for
a given sensor calibration and maximum expected irradiance. This is an
example only. Your values will be different.
This example uses the calibration provided by LI-COR, Inc. Assume that the
sensor calibration is 87 µA kW
-1 m 2 . The pyranometer outputs current which is
converted to voltage by the 100 Ω shunt resistor in the cable or on the wiring
panel. To convert the calibration from current to voltage, multiply the LI-COR
calibration by 0.1 K
Ω (shunt resistor). The example calibration changes to 8.7
mV kW -1 m 2 .
A reasonable estimate of maximum of irradiance at the earth's surface is 1 kW
m
-2 . Thus, an estimate of the maximum input voltage is obtained by
multiplying the calibration by the maximum expected irradiance. In this
example that product is 8.7 mV. Now, select the smallest input range which is
greater than the maximum expected input voltage. In this case the 25 mV slow
range for the CR10 and 15 mV slow range for the 21X are selected.
A.4 Multiplier
The multiplier converts the millivolt reading to engineering units. The most
common units and equations to calculate the multiplier are listed in Table
A.4-1.
TABLE A.4-1. Multipliers Required for Average Flux
and Total Flux Density for SI and
English Units for a LI200S Pyranometer
UNITS MULTIPLIER PROCESS
W m -2 (1/C) * 1000 Average
MJ m -2 t * (1/C) * 0.001 Total
kJ m -2 t * (1/C) Total
cal cm -2 min -1 (1/C) * (1.4333) Average
cal cm -2 t *(1/C) * (0.02389) Total
C = (LI-COR calibration) * 0.1
t = datalogger execution interval in seconds